Complex and extensive piping infrastructure systems are commonly used for high-volume transport of liquid media and gases over extended distances and multiple changes of elevation in various municipal and industrial applications. Examples of such piping infrastructures include public works for distribution of water to and within residential and industrial communities, collection, treatment and disposal of residential and industrial waste streams, movement of raw materials, reagents, products and waste streams within pulp and paper mills, transfer of crude oil and resulting petroleum products within refineries, and transport of natural gas. Reliable and efficient transport of liquid media and gases in such systems requires a plurality of strategically located pressure-regulating and monitoring service stations throughout the piping infrastructures to constantly maintain and control pressures applied to ensure target flow rates are maintained. Depending on the type of liquid material or gases being transported and on location within the piping infrastructure, a service module provided at a service station may contain one or more pieces of pressure-regulating and/or monitoring equipment such as single- or double-port main valves, pressure-reducing valves, pressure-relief and check valves, pumps, pump control valves, flow meters, and the like.
In most municipal water supply and waste disposal systems, the attendant piping infrastructure is buried underground and therefore the pressure-regulating and monitoring service stations are typically situated below ground within buried or subterranean concrete vaults. The walls of the vaults are provided with integrally installed inlets and outlets for engaging the piping infrastructure. The inlets and outlets are coupled to the requisite equipment installed within the vaults. Each service station is provided with bypass lines to enable shutdown and routine servicing of the equipment or, alternatively, replacement of failed or obsolete equipment. Such stations i.e., underground concrete vaults, are made just large enough to house the requisite equipment, one or two bypass lines and to provide the necessary minimal space for one or two workers to enter the station and perform the necessary service work. Access is typically provided through vertical openings provided in the tops of such vaults. The openings are commonly referred to as manholes, and are just large enough for a service worker to fit through. Such concrete vault service stations can be constructed on-site, that is by first constructing the vault by pouring the concrete walls and floor, the piping infrastructure inlet and outlet are integrally cast into the vault walls when the concrete is being poured, then installing the requisite equipment and bypass lines(s), and finally, connecting the service station into the flow of liquid media contained within the piping infrastructure. Alternatively, subterranean concrete vaults can be pre-cast and partially configured with equipment off-site, then trucked to their installation location within the piping infrastructure wherein they are installed and their construction and configuration is completed. Because of the interior space required for access and service work, such vaults are typically very heavy, e.g., 20,000-55,000 lbs (9,000-25,000 kg), they are commonly cast in two pieces and require heavy-duty specialized cranes, excavators and personnel for their handling and installation.
Federal and regional government agencies have designated such service stations, e.g., buried concrete vaults, as “confined spaces” wherein workers may encounter atmospheric hazards such as lack of oxygen or the presence of toxic vapours, and/or physical hazards such as electrical shock, mechanical malfunctions, or entrapment/engulfment by liquids or solids. “Confined spaces” are defined as spaces that are large enough for a person to enter through manhole or hatch covers, have limited means of entry or egress, and are not designed for extended human occupancy. Examples of such service stations include pumping stations, meter stations and valve stations. Entry into and service work inside “confined space” stations are strictly regulated under occupational safety legislation to ensure worker safety and rapid exit in case of emergencies.